Effects of Dietary Protein and Lipid Levels on Growth Performance, Muscle Composition, Immunity Index and Biochemical Index of the Greenfin Horse-Faced Filefish (Thamnaconus septentrionalis) Juvenile

The effects of different dietary protein and lipid levels on juvenile greenfin horse-faced filefish(Thamnaconus septentrionalis)was experimentally evaluated in a 56-day study.Fish(initial weight 6.47±0.56 g)were fed with nine different diet combinations containing three varying levels of protein(37%,43%,49%)and lipids(4%,7%,10%)in triplicates,where the protein-to-energy(P/E)ratios of the diets varied in the range of 19.17-26.99mgkJ−1.Results showed that fish fed diets containing 49%protein and 10%lipid exhibited significantly lower feed intake than those fed other diets.The weight gain of fish fed diets with 43%protein was significantly higher than that of fish fed 37%or 49%protein diets.While no significant change in weight gain was observed when lipid content was increased from 4%to 7%,weight gain decreased significantly when lipid increased from 7%to 10%.The protein efficiency ratio and feed efficiency were highest when the fish were fed the diet with 49%protein and 7%lipids.Muscle crude lipid content was positively correlated with dietary protein level regardless of lipid level.The diet of 43%protein or 7%lipids significantly reduced the activity of alanine aminotransferase and aspartate aminotransferase in liver.The contents of aspartate aminotransferase,superoxide dismutase and malondialdehyde were significantly increased from 4%to 10%lipids in plasma.The plasma total cholesterol and triglyceride contents were positively correlated with dietary lipid level at the same protein level.Our comprehensive analysis concluded that a diet with 43%protein and 7%lipid,with a P/E ratio of 23.07mgkJ−1,significantly promote the growth performance,feed utilization and health of juvenile greenfin horse-faced filefish.